Drexel RET Research Project Marshall Mosesson Moorestown H.S. Dr. Surya Kalidindi Drexel U. Mentor

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Drexel RET Research ProjectMarshall Mosesson
(Moorestown H.S.)Dr. Surya Kalidindi (Drexel U.
Mentor)

• Orientation Imaging Microscopy
• of Ti 6Al-4V

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Research Overview
Engineering Design

• An understanding of a polycrystalline
  materials underlying microstructure may allow
  engineers to modify strength parameters to meet
  custom demands.

Properties
Processes
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Research OverviewMaterial Processing

• Different methods of processing
  polycrystalline materials will change the
  microstructure and thereby affect the overall
  properties of the material
• Composition of Alloy
• Casting/molding conditions
• Annealing
• Re-crystallization
• Extruding
• Rolling
• Forging

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Microstructure Attributes
Question How can we link the processing of a
material to its strength characteristics?
Answer Examine the underlying grain
characteristics

• Grain size and shape.
• Grain boundary parameters.
• Grain composition (amount of each element).
• Chemical phase of the grain.
• Crystal orientation of the grain with respect to
  its neighbors.
• Dislocation amount in grains.

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Orientation Imaging Microscopy (OIM)
The following presentation ( blue background
slides) gives a description of OIM along with a
variety of applications of OIM to materials
problems. OIM is based on automatic indexing of
Electron BackScatter Diffraction patterns which
can be produced in a properly equipped scanning
electron microscope. OIM provides a complete
description of the crystallographic orientations
in polycrystalline materials. This enables the
effects of crystal orientations on materials
properties to be studied in a manner that has
been previously inaccessible to materials
scientists.
The OIM slides were created by
TexSEM Laboratories TSL / EDAX Draper, Utah USA
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Electron Backscatter Diffraction in the SEM
Electron backscatter diffraction patterns (or
EBSPs) are obtained in the Scanning Electron
Microscope (SEM) by focusing a stationary
electron beam on a crystalline sample. The sample
is tilted to approximately 70 degrees with
respect to the horizontal. The diffraction
pattern is imaged on a phosphor screen. The image
is captured using a low-light SIT camera. The
bands in the pattern represent reflecting planes
in the diffracting crystal volume. Thus, the
geometrical arrangement of the bands is a
function of the orientation of the diffracting
crystal lattice.
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Image Formation Kinematic Theory
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Image Processing
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Image Processing
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Crystallography and Microstructure
As the beam is moved from grain to grain the
electron backscatter diffraction pattern (EBSP)
will change due to the change in orientation of
the crystal lattice in the diffracting volume
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Automatic Indexing of EBSPs
An image processing algorithm (Hough Transform)
is used to detect bands in the diffraction
pattern. The pattern can be indexed by comparing
the angles between the detected bands to a
theoretical look-up-table. Indexing the pattern
allows the crystallographic orientation to be
determined. The image capture/band
detection/indexing cycle can be done
automatically in a fraction of second.
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Orientation Imaging Microscopy (OIM) Schematic
In an OIM scan the beam is stepped across the
sample surface in a regular grid. At each point
the EBSP is captured and automatically indexed
and the orientation and other information
recorded (such as the pattern quality of the
EBSP, an indexing reliability factor, the
secondary detector intensity and EDS data.)
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Creating OIM Images
A Grain Boundary Map can be generated by
comparing the orientation between each pair of
neighboring points in an OIM scan. A line is
drawn separating a pair of points if the
difference in orientation between the points
exceeds a given tolerance angle. An Orientation
Map is generated by shading each point in the OIM
scan according to some parameter reflecting the
orientation at each point. Both of these maps are
shown overlaid on the digital micrograph from the
SEM.
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Boundaries - Coincident Site Lattice (CSL)
In this OIM map the boundaries are colored
according to a particular type of coincident site
boundary. (A black boundary indicates no
correspondence with a coincidence boundary.) The
higher the coincidence boundary type, the less
ordered the boundary is considered to be.
Coincident site boundaries have been observed to
confer special mechanical properties to the
material.
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Phase Identification
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Drexel University Research ProjectOverview

• Introduction to the use of all equipment used.
• Sample preparation for imaging
• Cutting
• Bakelite mounting
• Grinding and polishing
• Etching and re-polishing
• Micro-Hardness indentations for referencing
• locations on the sample
• Carbon painting and mounting for ESEM imaging
• OIM imaging for grain orientation
• EDS imaging for element analysis

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Sample Preparation

• Cut a 1 cm cube with the Diamond cut off wheel.
• Mount the cube in a bakelite cylinder (Mounting)
• Grind and polish the sample surface.
• Acid etch to reveal grain boundaries for
  examination using an optical metallograph.

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Sample Preparation Continued

• Re-Polish the etched sample.
• Optically image to gauge surface smoothness.
• Create micro-hardness indentations as a
  reference grid on the sample surface.

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Titanium 6Al-4VOptical Microscopy

• Light microscopy at 1000x of a smooth surface
  after acid etching to reveal grain shapes.

The background image was magnified at 1000x
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Slide Show of My Research of Ti-6Al-4V by
Optical Microscopy
1000x Mag Optical image after polishing with 1 mm
colloidal silica.
1000x Mag Optical image after acid etching to
reveal grain structure.
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Ti-6Al-4V Sample After Micro-indentation
Optical image at 100x
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Ti-6Al-4V Sample After OIM Imaging Research
ESEM image of a reference grid of
micro-indentations. Each side of the square grid
is 200mm long. The fine points are hydrocarbon
deposits as a consequence incident electron beam
interaction with sample surface.
KeV 20.0 Mag 350 Tilt 0.0
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The Drexel Environmental Scanning Electron
Microscope (ESEM)EDAX Model XL 30
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Sample mounted in the ESEM for EDS analysis
View of open sample chamber
Ti sample mounted in bakelite
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OIM analysis sample holder for the ESEM
Ti sample was attached to the 70 degree sample
holder by conductive carbon adhesive tape.
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Computer controls for the ESEM
EDS analysis shown on the monitor
Sample chamber and digital controls can be seen
on the monitor
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David Von Rohr feeding the ESEMwith liquid
nitrogen so it can keep the Si(Li) detector cool
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Ti-6Al-4V Kikuchi back scattered diffraction
pattern without enhancement or indexing
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OIM analysis of Ti-6Al-4V
Indexed Kikuchi back-scattered diffraction
pattern
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Pole Figure of Ti-6Al-4V from OIM analysis
This figure shows the crystal orientations
indexed by color in reference to the OIM map.
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Orientation map of Ti-6Al-4V Sample
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OIM analysis of grain orientation
Crystal orientations of each grain
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Ti-6Al-4V color map showing orientations changes
across individual grains.
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Grain Boundary Map
Angle between grains are indicated by the colored
lines
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EDS analysis of Ti-6Al-4V showing elements in
sample
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EDS analysis of Ti-6Al-4V Showing Element
Abundances (in a small region)
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Acknowledgements

• I wish to thank the following people for their
  kind help
• Dr. Mun Choi RET Grant director
• Dr. Surya Kalidindi my faculty mentor
• Materials faculty who broadened my experience
  Dr. Rick Knight, and Dr. Yuri Gogotsi
• Gwenaelle Proust my graduate student mentor
• David Von Rohr Materials Microscopist
• Stephanos Karas Computer Network Sysop
• Joanne Ferroni RET coordinator and our
  photographer
• Graduate students who helped in numerous ways
  Josh Houskamp, Jing Zhang, Beth Carroll, Svetlana
  Dimovski, Nevin Naguib
• Fellow RET Research Fellows for putting up
  with me
• Andy Benzing who trusted me with his 500
  digital camera